The invention relates to a cardiac output and right ventricular ejection fraction computer which measures a cardiac output, a right ventricular ejection fraction, and a right ventricular end-diastolic volume which are the subjects of hemodynamic study.
Methods of measuring the right ventricular ejection fraction in the hemodynamic study which have heretofore been known include: RI angiography, X-ray angiography, ultrasonic echocardiography, and an indicator dilution method.
The RI angiography measures the right ventricular ejection fraction by injecting a radioisotope into the body and it exhibits a high degree of measurement accuracy. However, measurement must be made within an IR administration area, which makes the method somewhat cumbersome. In addition, the method does not allow frequent measurements, giving consideration to the influence of the injected radioisotope on the body.
The X-ray angiography and the ultrasonic echocardiography are methods for calculating the right ventricular ejection fraction through image analysis. In measurements based on these methods the form of, e.g., the left ventricle can be approximated as an ellipse of revolution, while the form of the right ventricle cannot be approximated due to its anatomic complexities.
The indicator dilution method, particularly, a thermodilution method, measures the right ventricular ejection fraction by leaving a thermodilution catheter in the body when making a measurement by right ventricular catheterization. Thus, the measurement is relatively simple and easy. In the calculation of the right ventricular ejection fraction by the thermodilution method, a plateau method and an exponential method are known.
The plateau method calculates the ejection fraction from differences between four successive end-diastolic plateaus produced in the decay line of a thermodilution curve and a base line, measures the ejection fractions over four beats, and averages the three calculated ejection fractions to obtain the ejection fraction of the thermodilution curve.
The exponential method synchronizes an R wave of an ECG with the plateaus produced in the decay line of a thermodilution curve, derives an exponential function from the decay curve of the thermodilution curve, and calculates a Lime constant of this measuring system to obtain the ejection fraction.
By the way, to calculate the right ventricular ejection fraction by the plateau method in a thermodilution method-based measurement, the larger the ejection fraction is, the greater errors the ejection fractions calculated every ejection exhibit. As a result, the calculated average of four ejections becomes smaller than the actual value.
This error is caused by the fact that substantially 0.degree. C.-cold water consisting of physiological saline or 5% dextran used as an indicator (injectate) remains within the catheter and that the vessel wall and myocardiac wall are cooled through the catheter wall. Therefore, it is the catheter insert length that determines the degree of an error. This can be said from the result of the investigation of a model that the ejection fraction obtained from a thermodilution curve that is measured by directly injecting an indicator from the right ventricle of the model exhibited no error.
As shown in FIG. 10, (a) shows an exemplary thermodilution curve when the catheter insert length is 90 cm, while (b) shows a thermodilution curve in which only the influence of the catheter in cooling the vessel wall and myocardiac wall is plotted.
In FIG. 10, let it be assumed that temperature variations caused by cold injectate in four beats are A, B, C, D, and that temperature variations caused by a negative heat produced by the injectate remaining in the catheter through the catheter wall that remains within the body are a, b, c, d. In addition, when EQU A'=A+a B'=B+b EQU C'=C+c D'=D+d
ejection fractions EF.sub.1, EF.sub.2, EF.sub.3 each ejection are conventionally calculated as: EQU EF.sub.1 =1-B'/A' EQU EF.sub.2 =1-C'/B' EQU EF.sub.2 =1-D'/C'
Errors resulting because the influence of the catheter in cooling the vessel wall and myocardiac wall was not considered.
The invention has been proposed to overcome the above problems and has as an object the provision of a cardiac output and right ventricular ejection fraction system which is capable of correcting the influence of the catheter in cooling the vessel wall and myocardiac wall and of implementing highly accurate measurement when measuring ejection fractions and the like while calculating the thermodilution curve by the plateau method, the thermodilution curve being obtained by the thermodilution method.